The present invention relates generally to the evaluation and optimization of software receivers for spread spectrum signals of Global Navigation Satellite Systems (GNSSs). More particularly the invention relates to a system, method, and computer program product for testing a GNSS receiver design.
Many examples of GNSSs exist. Presently, the Global Positioning System (GPS; U.S. Government) is the dominant system; however alternative systems are expected to gain increased importance in the future. So far, the GLObal NAvigation Satellite System (GLONASS; Russian Federation Ministry of Defense) and the Galileo system (the European programme for global navigation services) constitute the major alternative GNSSs. Various systems also exist for enhancing the coverage, the availability and/or the quality of at least one GNSS in a specific region. The Quasi-Zenith Satellite System (QZSS; Advanced Space Business Corporation in Japan), the Wide Area Augmentation System (WAAS; The U.S. Federal Aviation Administration and the Department of Transportation) and the European Geostationary Navigation Overlay Service (EGNOS; a joint project of the European Space Agency, the European Commission and Eurocontrol—the European Organisation for the Safety of Air Navigation) represent examples of such augmentation systems for GPS, and in the latter case GPS and GLONASS.
To ensure good performance and reliability of a GNSS receiver, its design must be tested thoroughly. The traditional way to test the real-world performance of a GNSS receiver is to arrange the receiver in a vehicle (or a portable pack) and drive, walk or by other means move the receiver around an area of interest (typically a challenging environment, such as a so-called urban canyon), record position data, and then plot the trajectory on a map and evaluate the trajectory visually.
A refined version of this strategy may involve employing a so-called GPS/INS (Inertial Navigation System) truth reference. Such a system combines relative positioning measurements from an inertial measurement unit (IMU) with available position data from a high-grade GPS receiver to provide continuous absolute position data in all environments. Specifically, this reference data is highly accurate because precise relative measurements from accelerometers and gyroscopes of the IMU can be used whenever the GPS signals are degraded or unavailable. The GPS/INS is carried or driven along with a RUT (receiver under test), and produces a reference trajectory against which the navigation data generated by the RUT is compared. This enables a quantitative measurement of position accuracy. For example, a two-dimensional error can be calculated at time-aligned points, which in turn may serve as a basis for statistics like mean, 95th percentile, and maximum errors for the duration of the trial.
For completeness, it may be worth mentioning that it is not desirable to replace GNSS receivers on the market with high-grade GPS/INS units to overcome any inaccuracy problems with the GNSS receivers. Namely, a GPS/INS unit of sufficient quality is very bulky and heavy. Such a unit also requires considerable amounts of power, and perhaps most important, costs many orders of magnitude more than a conventional GNSS receiver.
The first traditional method is problematic because it is inherently subjective. Different receivers often have different strong and weak points in their navigation algorithms. It is therefore difficult to decide which design is better over the course of a long trial. Also, an accurate evaluation of a trial generally requires some firsthand knowledge of the test area. Unless relevant maps are available in sufficiently high resolution, it is difficult to tell, for example, how accurate a trajectory along a wooded area might be. The second traditional method is a significant improvement upon the first, since it introduces an objective, quantitative reference against which to evaluate positioning and navigation performance of the proposed receiver design.
However both methods suffer from one fundamental limitation: results are inherently obtainable only in real time (plus evaluation in the lab). Moreover, the scope of test coverage is limited to the number of receivers that can be simultaneously fixed on a test rig. A reasonable number of receivers to test concurrently lies on the order of five to ten. Thus, a test car outfitted with this many receivers will be able to generate five to ten quasi-independent results per outing. If a larger number of receivers is to be tested multiple outings are required. Naturally, this may become cumbersome, expensive and time-consuming. Furthermore, trials run at different times necessarily present different signal conditions to the pool of receivers under test, which makes direct comparisons of receiver quality somewhat less meaningful.